I try to debrick my Kindle 4 NT. I followed instruction in guide for "noobs", everything was ok till I got to Mfg tool. I selected "kindle fastboot", pressed "start"and after few sec mfg tool showed "please connect device" so I don't get anywhere. I am novice in this... for a year I was using kindle for reading and not booting

You did not provide enough details to determine which of many possible problems may have happened. Perhaps MfgTool did not see a kindle attached in USB Downloader mode because you had successfully switched it to fastboot mode just like you told it to do...